A Modified Posterior Wedge Osteotomy with Interbody Fusion for the Treatment of Thoracolumbar Kyphosis with Andersson Lesions in Ankylosing Spondylitis: A 5-Year Follow-Up Study
Ankylosing spondylitis (AS) is a chronic inflammatory disease that primarily affects the spine, leading to progressive rigidity and osteoporosis. One of the severe complications of AS is the development of Andersson lesions (ALs), also known as spondylodiscitis, destructive vertebral lesions, or spinal pseudarthrosis. These lesions often result in mechanical pain, kyphotic deformity, and neurologic deficits, necessitating surgical intervention. This study aims to evaluate the safety, efficacy, and feasibility of a modified posterior wedge osteotomy with interbody fusion for treating thoracolumbar kyphosis with ALs in AS patients.
Introduction
AS patients are prone to spinal fractures due to progressive rigidity and osteoporosis, which can occur even with minor trauma or spontaneously. Persistent motion and repeated inflammatory stimuli at the fracture site can lead to non-union, resulting in pseudarthrosis or ALs. The prevalence of ALs in AS ranges from 1.5% to 28%. Early-stage ALs are challenging to diagnose due to symptom similarity with AS-related back pain, often requiring computed tomography (CT) and magnetic resonance imaging (MRI) for confirmation. Delayed management can lead to progressive kyphotic deformity and neurologic deficits, making conservative treatments unsuitable. Surgical intervention is considered the most effective management for correcting kyphosis and restoring sagittal balance.
Methods
This retrospective study included 23 AS patients (18 males, 5 females) with an average age of 44.8 years (range 25–69 years) who underwent modified posterior wedge osteotomy from June 2008 to January 2013. All patients had thoracolumbar kyphosis with ALs and were followed up for an average of 61.4 months (range 45–80 months). Sagittal balance parameters, including thoracic kyphosis (TK), thoracolumbar kyphosis (TLK), lumbar lordosis (LL), and sagittal vertical axis (SVA), were assessed using standing lateral radiography of the whole spine. Radiologic fusion was evaluated using the Bridwell interbody fusion grading system. Clinical outcomes were measured using the visual analog scale (VAS) for back pain and the Ankylosing Spondylitis Quality of Life (ASQoL) questionnaire. Neurologic deficits were assessed using the American Spinal Injury Association (ASIA) grading system.
Surgical Technique
The surgical procedure involved placing the patient in a prone position on an adjustable spine frame. Pedicle screws were inserted 2 to 3 levels above and below the lesion using C-arm X-ray guidance. The modified posterior wedge osteotomy included resection of the affected intervertebral disc, cartilage endplate, and a segment of the posterior vertebral body. The osteotomy was closed by slowly extending the spine frame while applying compressive pressure on the pedicle screws. The anterior cavity was filled with autologous or artificial bone via a transforaminal approach, followed by posterolateral bone grafting. Somatosensory-evoked potentials and motor-evoked potentials were monitored throughout the procedure. Patients were allowed to walk one week post-surgery while wearing a brace for at least three months until complete bone fusion was achieved.
Results
The mean operative duration was 205.4 minutes (range 115–375 minutes), with an average blood loss of 488.5 mL (range 215–880 mL). Dural tears with cerebrospinal fluid leakage occurred in three cases, managed intraoperatively with fascia tissue and lumbar drainage. No other complications, such as neurologic injury, wound infection, fixation failure, or main vascular injury, were observed.
Clinical Outcomes
Significant improvements were observed in VAS and ASQoL scores. The VAS score decreased from 7.52 ± 1.31 pre-operatively to 1.70 ± 0.70 at the final follow-up (P < 0.001). The ASQoL score improved from 13.87 ± 1.89 pre-operatively to 7.22 ± 1.24 at the final follow-up (P < 0.001). Neurologic deficits improved in all patients, with one ASIA B patient recovering to ASIA C, two ASIA C patients improving to ASIA D, and six ASIA D patients improving to ASIA E.
Radiologic Outcomes
Significant improvements were noted in all sagittal balance parameters. The TLK decreased from 40.03 ± 17.61° pre-operatively to 13.86 ± 6.65° post-operatively and 28.45 ± 6.63° at the final follow-up (P < 0.001). The TK decreased from 52.30 ± 17.62° pre-operatively to 27.76 ± 6.50° post-operatively and 28.45 ± 6.63° at the final follow-up (P < 0.001). The LL improved from -29.56 ± 9.73° pre-operatively to -20.58 ± 9.71° post-operatively and -20.73 ± 10.27° at the final follow-up (P < 0.001). The SVA improved from 11.82 ± 4.55 cm pre-operatively to 5.12 ± 2.42 cm post-operatively and 5.03 ± 2.29 cm at the final follow-up (P < 0.001). No significant loss of correction was observed between post-operative and final follow-up measurements.
Discussion
ALs in AS patients can be classified into three types based on their etiology and pathology: localized lesions, extensive lesions without fractured posterior elements, and extensive lesions with fractured posterior elements. The thoracolumbar junction is the most common site for pseudarthrosis due to increased local stresses. Various surgical techniques, including Smith-Petersen osteotomy (SPO) and pedicle subtraction osteotomy (PSO), have been used to correct kyphotic deformity in AS patients. However, these techniques have limitations, such as increased risk of implant failure, delayed union, and severe neurovascular complications.
The modified posterior wedge osteotomy described in this study addresses these limitations by allowing more effective kyphosis correction through greater debridement of destructive lesions and wider resection of posterior elements. This technique also ensures solid fusion by setting the inferior bony endplate of the upper vertebra on the cancellous bone of the remaining vertebra. Adequate anterior bone grafting after osteotomy maintains intervertebral height, increases kyphotic correction, and reduces stress on internal fixation, thereby reducing the risk of complications.
Compared to traditional PSO, the modified posterior wedge osteotomy results in significantly lower blood loss and operative time. The radiologic union was achieved after a mean of 4.3 months without instrumentation complications, similar to previous reports. Solid bone fusion was achieved in all patients, with no loss of correction observed at the final follow-up.
Conclusion
The modified posterior wedge osteotomy with interbody fusion is an effective and safe surgical procedure for treating thoracolumbar kyphosis with ALs in AS patients. This technique provides satisfactory correction of local kyphosis, solid bone fusion, and significant relief of back pain, with reduced blood loss and operative time. The study highlights the importance of considering lesion characteristics and pathology when selecting surgical techniques for AS patients with ALs.
doi.org/10.1097/CM9.0000000000000594
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